3-500Z vs 3-500ZG

[Multi-Volti Devices]

I's say that if he needs to replace one, then he should have more power
output, assuming the one needing replacement was soft, but maybe that's
missing your point.

I would be reluctant to mix 3-500 manufacturers tubes for reasons listed
below.

I haven't looked at any Russian tubes, but remember that Penta used to
be using Chinese tubes (Sino, if I remember). A few years ago, the rumor
was that there were three factories, and one produced good product if
they would survive the initial 48 hours of operation, the second plant
was so-so, and the third really bad news. I saw one tube that had the
anode assembly  mounted crooked (maybe a 10 degree tilt?) on the anode
rod coming out the top. It worked, but sure was unnerving to look at!

I was told by RichMeasures AG6K, that the Chinese tubes were a copy of
the Amperex tube, which by the way was the only graphite anode 3-400 I
ever saw, years ago. According to Rich, the Amperex and old Eimacs had a
mu of around 200, and that Eimac dropped mu to 160, if my memory is
intact. This was supposedly to reduce the possibility of parasitic
oscillations. Rich's series of SB-220 articles and vaporized bandswitch
wafers was very interesting and he observed that the Amperex-copied
Chinese tubes were more prone to doing that. NOT BECAUSE THEY WERE BAD!
but because they had higher gain. He seemed to feelthat if you could
find Amperex tubes (they were much more expensive that Eimac, probably
for distribution channel reasons), they would probably exhibit the same
behavior of amps with poor parasitic suppression.

Having tubes of mixed mu is probably not a good idea.

I have heard good things about Svetlana, in general, but Eimac has
always been an outstanding company that stands behind their outstanding
product.

Any interested readers out there may want to dig up those SB-220
articles. I never saw many blown up SB-220's at Heath, but the SB-1000
(operating at higher voltage and gain) and it's twin the old AL-80 had
the problem of bandswitch vaporization due to apparent parasitics.

Murray





Rod Fitz-Randolph wrote:

> Not sure about the 3-500ZG designation but I am referring to the
> graphite plate 3-500s.
>
> My friend, WA4VWR, needs to replace a 3-500Z in his SB-220.  He
> doesn't
> believe he should just replace one single 3-500Z with a 3-500ZG but
> he wants to know, if he replaces both of his Eimac 3-500Zs with the
> 3-500ZGs, will he get less than, the same as, or more rf output with
> the exact same driving power?  It's a good question that I certainly
> didn't have the background to answer.
>
> Is there someone out there that may have replaced the 3-500Zs in a
> SB-220
> or a Drake L4B that can answer the question for him.
>
> Also, (on my own), is there only a single graphite-plate 3-500
> manufacturer
> and, if there is more than one, which one has the best
> reputation/track
> record?
>
> Thank you very much.
>
> Rod, N5HV
> w5hvv at aeneas.net


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